"They’d gone north and were able to find less expensive real estate and draw upon talent from the city and the peninsula."

After YouTube's move, other startups moved even further north.

You've heard of a few of them: Zynga, Dropbox, and Twitter are among the biggest names.

The appeal of San Francisco was the city itself. Though it has sneakily horrible weather (no summer), it is fairly walkable and cosmopolitan. That attracted talented and young workers. Also, building a startup in the city wasn't that expensive. There were underdeveloped areas where the rent wouldn't turn up the heat too much on your burn rate.

That's changing.

Correction: An earlier version of this story said Eventbrite's rent tripled. In fact, Julia Hartz said: "The rents that we paid two years ago have tripled now in the span of two years. " A spokesperson contacted us to clarify that what she meant was that the place where Eventbrite was renting before now go for 3X as much as it did. Eventbrite is no longer in that space. It's moving to a new one.